Compressed natural gas (CNG) is a high octane fuel that is beneficial for reducing engine knock, for reducing hydrocarbon emissions in cold start events, and for reducing carbon dioxide emissions during engine operations. However, CNG has a low energy density compared to liquid hydrocarbon fuels, such as diesel fuel or gasoline. This typically requires packaging of CNG in cryogenic quality tanks (as liquified natural gas (LNG)) or in high pressure tanks (approximately 200-250 atmospheres).
To increase the range and total fuel quantity stored in a vehicle, CNG may be utilized in conjunction with gasoline or diesel fuel, requiring the vehicle to switch between fuels for optimal performance. However, space constraints do not allow for the inclusion of separate fuel tanks to all vehicles. A preferable system may be one that stores liquid fuel and pressurized gaseous fuel together in a single tank. In particular, CNG is able to partially dissolve in gasoline or diesel fuel when stored together at a relatively low pressure (˜100 atm).
Storing a mix of pressurized gaseous fuel and low pressure liquid fuel within a single tank presents challenges for refueling. It may be possible to add liquid fuel to the tank first, then pressurize the tank with pressurized gaseous fuel, or to add a pre-pressurized fuel mix. However, it may not always be practical to empty the tank completely before refueling, and pre-pressurized fuel mixtures may not always be available at refueling stations. Current refueling systems do not allow for the addition of either pressurized gaseous fuel or low pressure liquid fuel or a pre-pressurized fuel mix to a single tank when refueling and/or as fuel is available at refueling stations.
The inventors herein have recognized the above problems, and developed systems and methods to at least partially address these issues. In one example, a fuel tank system, comprising: a fuel tank configured to store a liquid fuel and a pressurized gaseous fuel capable of partially dissolving in the liquid fuel; a refueling conduit coupled to the fuel tank via a tank access valve; a first high pressure refueling port coupled to the refueling conduit; a low pressure refueling port coupled to the refueling conduit via a check valve. In this way, pressurized gaseous fuel or a pre-pressurized mix of fuels may be added to the fuel tank without active control any time the fuel pressure in the fuel tank is below a maximum allowable pressure, and liquid fuel may be added to the fuel tank with active control whenever the fuel pressure and liquid fuel level in the fuel tank are below threshold levels.
In another example, a method for refueling a vehicle fuel tank, comprising: responsive to a first condition, pumping liquid fuel from a surge tank into a fuel tank, while storing a liquid fuel and a pressurized gaseous fuel only partially dissolved in the liquid fuel in the tank. In this way, liquid fuel can be added to a fuel tank without requiring the tank pressure to approach zero, allowing for more opportunities to add liquid fuel to the fuel tank.
In yet another example, a method for refueling a vehicle fuel tank, comprising: responsive to a first condition, pumping gaseous fuel from a fuel tank into a secondary vapor tank, while storing a liquid fuel and a pressurized gaseous fuel only partially dissolved in the liquid fuel in the tank. In this way, a mixed fuel tank may be relieved of a high pressure, allowing for the addition of liquid fuel without combusting additional gaseous fuel.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.